Normally ASE will not disconnect an IDLE client as long as the periodic TCP/IP handshake is OK.
If client itself disconnects, the SPID in ASE will survive for some time until TCP/IP says no handshake. Then the server will clean up. But this is not same as IDLE connection.
Check with your DBA/SysAdmin if there is a watchdog process that terminates idle connection.
Connection is a resource use in some form. So it should NOT be idling beyond a reasonable time.
HTH
Avinash